Typically, a valve train for an internal combustion engine includes one or more valves, a camshaft having one or more cam lobes, and a follower contacting each cam lobe and valve. The valve train may also include a hydraulic lash adjuster, which may serve as a pivot for a finger type cam follower.
Variable valve actuation mechanisms have been extensively developed and to some extent utilized to improve efficiency of the internal combustion engine, also to improve idle stability, power output, and emissions. These improvements are achieved by controllably varying the valve lift, timing, and duration. The ability to vary one or more of these valve-event attributes, either discretely or continuously depends on the complexity of the actuating mechanism. For an overhead-cam valvetrain employing a finger follower, discrete variations in the valve lift profile can be achieved by cam-lobe switching. However, cam-lobe switching mechanisms are complicated and bulky because they require at least three follower surfaces where outer surfaces are required to maintain balance with one existing pivot point, and only one of the three surfaces is likely to be a rolling type due to limited available total width. The two outer follower surfaces are usually of a sliding type, each having a small width with high specific loading. In addition, these mechanisms require a high-pressure oil supply for actuation of different segments of the follower corresponding to cam lobes being switched. This necessitates machining of additional oil passages.
For an overhead-cam valve train employing a finger follower, the pivot support element, which may also serve as a lash adjuster, could provide valve de-activation. A mechanism, employing two concentric bodies with a freedom for axial relative motion, can be actuated to switch between a fully-extended and a fully-collapsed position. Spring-biased pins located on one body can be hydraulically displaced to engage into receiving holes on the other body for holding in the fully-extended position. However, a pin-engagement mechanism requires precise alignment of the pins with the receiving holes. Furthermore, a pin-engagement mechanism lacks the flexibility to yield intermediate positions between the fully extended and the fully collapsed limits.
As a result, it is desirable to provide a valve actuator assembly for an engine that has valve-deactivation for an overhead-cam valve train. It is also desirable to provide a valve actuator assembly for an engine that has discrete-step variable valve actuation. Therefore, there is a need in the art to provide a valve actuator assembly for an engine that meets these desires.